Sequential fuel injection systems have heretofore been proposed using one electrically operated valve for each cylinder to allow flow of a controlled amount of fuel during each intake stroke with the amount of fuel being controlled by controlling the duration of electrical pulses applied through distributor means to allocate the application of the pulses to the injector valves in accordance with the firing order of the engine. Such systems have not been entirely satisfactory with respect to construction, operation and reliability. For example, one problem is that the optimum amount of fuel varies according to non-linear characteristics of engine speed and engine intake manifold pressure and with prior art systems, considerable juggling of adjustments has been required in attempting to satisfy the optimum requirements. The setting of controls to obtain optimum operation under one particular set of conditions usually results in considerable error when the operating conditions are substantially different and settings coming close to the ideal requirements are possible only after considerable and lengthy trial and error procedures. In addition, even after the ideal settings are determined, it is difficult to reproduce the system from a manufacturing standpoint due to variations in the values of components in the system.